US20130079763A1 - Logarithmic Amplifier, Electrosurgical Generator Including Same, and Method of Controlling Electrosurgical Generator Using Same - Google Patents

Abstract

An electrosurgical generator includes an RF output stage, a current sensor, a voltage sensor, first and second log amplifiers, and a controller. The RF output stage is configured to supply electrosurgical energy to tissue. The current sensor is configured to sense a current of the electrosurgical energy and generate a current signal corresponding to the current of the electrosurgical energy. The first log amplifier is configured to amplify and compress the current signal. The voltage sensor is configured to sense a voltage of the electrosurgical energy and generate a voltage signal in response thereto. The second log amplifier is configured to amplify and compress the voltage signal. The controller is configured to receive the amplified voltage signal and the amplified current signal and operatively control the generation of the electrosurgical energy as a function of the amplified voltage signal and the amplified current signal.

Description

BACKGROUND
• 1. Technical Field
• The present disclosure relates to electrosurgery. More particularly, the present disclosure relates to a logarithmic amplifier, an electrosurgical generator including the same, and a method of controlling an electrosurgical generator using the same.
• 2. Discussion of Related Art
• Electrosurgery is the application of electricity and/or electromagnetic energy to cut, dissect, ablate, coagulate, cauterize, seal or otherwise treat biological tissue during a surgical procedure. Generally, electrosurgery utilizes an electrosurgical generator operable to output energy and active and return electrodes that are electrically connected via a cable assembly to the generator. The electrosurgical generator generates an electromagnetic wave (referred to herein as “electrosurgical energy”), typically above 100 kilohertz, between the active and return electrodes when applied to tissue. The electromagnetic wave created therebetween dissipates energy as heat as it travels between the electrodes. The electrosurgical energy usually has a frequency above 100 kilohertz to avoid muscle and/or nerve stimulation.
• During electrosurgery, current generated by the electrosurgical generator is conducted through the patient's tissue disposed between the two electrodes. The current causes the tissue to heat up as the electromagnetic wave overcomes the tissue's impedance. Although many other variables affect the total heating of the tissue, usually more current density correlates to increased heating.
• A variety of types of instruments utilizing electromagnetic radiation have been employed for various types of monopolar and bipolar electrosurgery. The basic purpose of both monopolar and bipolar electrosurgery is to produce heat to achieve the desired tissue/clinical effect. In monopolar electrosurgery, devices use an instrument with a single, active electrode to deliver energy from an electrosurgical generator to tissue, and a patient return electrode or pad that is attached externally to the patient (e.g., a plate positioned on the patient's thigh or back) as the means to complete the electrical circuit between the electrosurgical generator and the patient. When the electrosurgical energy is applied, the energy travels from the active electrode, to the surgical site, through the patient and to the return electrode. In bipolar electrosurgery, both the active electrode and return electrode functions are performed at the site of surgery. Bipolar electrosurgical devices include two electrodes that are located in proximity to one another for the application of current between their surfaces. Bipolar electrosurgical current travels from one electrode, through the intervening tissue to the other electrode to complete the electrical circuit. Bipolar instruments generally include end-effectors, such as grippers, cutters, forceps, dissectors and the like.
• Electrosurgical generators apply various currents, voltages and frequencies to achieve various tissue effects. The current, voltage, and frequency may be varied to achieve a target tissue impedance, a target power, a target voltage, and the like. These target values are generally based upon the surgical procedure to be performed, tissue characteristics, and/or the desired tissue/clinical effect. Electrosurgical generators employ one or more control systems to achieve these target values and to prevent the electrosurgical generator from operating outside predetermined constraints.
SUMMARY
• Electromagnetic energy is generally classified by increasing energy or decreasing wavelength into radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma-rays. As it is used in this description, “transmission line” generally refers to any transmission medium that can be used for the propagation of signals from one point to another.
• Although the following description describes the use of logarithmic amplifiers to compress a large output range of a generator to a small feedback range, the teachings of the present disclosure may also apply to a variety of applications where signals of large dynamic range may be encountered.
• According to an aspect, a control system for controlling a generator is provided. The control system includes a sensor, a log amplifier, and a controller. The sensor generates a sensor signal. The sensor may be a voltage sensor or a current sensor. The log amplifier is coupled to the sensor and amplifies the sensor signal. The controller generates an output signal as a function of the amplified sensor signal. In some aspects, the control system further includes a summer to sum a setpoint and the negation of the amplified signal from the log amplifier. The controller may be adapted to generate electrosurgical energy, i.e., the output signal may be electrosurgical energy. The generator may be an electrosurgical generator. The electrosurgical generator may be a portable electrosurgical generator coupled to a portable surgical instrument. In other embodiments, the generator may be an ultrasonic generator or a microwave generator.
• In any of the aspects, the control system includes a summer. The summer sums a setpoint and a negation of the amplified signal from the log amplifier to generate an error. The controller may generate the output signal as a function of the error.
• In any of the aspects, the control system includes a voltage sensor having a plurality of capacitors. The plurality of capacitors forms a voltage divider network that is in electrical communication with the output signal. The sensor signal may be a voltage of a capacitor of the divider network.
• According to another aspect of the present disclosure, the controller is a proportional-integral-derivative controller. The proportional-integral-derivative controller may have one or more variable gain coefficients. The proportional-integral-derivative controller can vary a proportional gain coefficient, an integral gain coefficient, and a derivative gain coefficient. One or more gain coefficients may be varied as a function of the amplified sensor signal. The controller may convert the amplified sensor signal to an RMS value or to an antilog of the amplified sensor signal.
• In any of the aspects, an electrosurgical generator includes an RF output stage, a current sensor, first and second log amplifiers, a voltage sensor and a controller. The RF output stage supplies electrosurgical energy to tissue. The current sensor senses a current of the electrosurgical energy. The voltage sensor senses a voltage of the electrosurgical energy. The first log amplifier amplifies the current signal. The second log amplifier amplifiers the voltage signal. The controller receives the amplified voltage and current signals. The controller may be configured to control the generation of the electrosurgical energy as a function of the amplified voltage signal and/or the amplified current signal.
• In any of the aspects, the controller may be configured to calculate the sum of a log voltage signal and a log current signal to compute a measured log power. The controller may be further configured to compare the measured log power against a target log power to compute an error signal.
• In any of the aspects, the electrosurgical generator may include a plurality of capacitors forming a capacitor divider network coupled to the RF output stage for measuring voltage of the electrosurgical energy.
• In any of the aspects, voltage sensor may include a plurality of capacitors that form a capacitor divider network. The capacitor divider network is in electrical communication with the electrosurgical energy. Additionally or alternatively, the capacitor divider network may be coupled to the RF output stage.
• In any of the aspects, the electrosurgical generator may include a dual directional coupler adapted for measurement of forward and reflective voltage.
• In any of the aspects, the controller is a proportional-integral-derivative controller. The proportional-integral-derivative controller may employ one or more variable gain coefficients. The proportional-integral-derivative controller may be configured to vary a proportional gain coefficient, an integral gain coefficient, and/or a derivative gain coefficient. The proportional-integral-derivative controller may include one or more look-up tables to vary one or more gain coefficients. One or more gain coefficients may be determined using an affine algorithm. In any of the aspects, a measured log power may be compared against a target log power to compute an error signal used by the proportional-integral-derivative controller.
• In any of the aspects, a gain coefficient may be varied as a function of the amplified voltage signal and/or the amplified current signal. The proportional-integral-derivative controller may have a setpoint of log power, log impedance, log current, or log voltage. The controller may be configured to calculate the log power by adding the amplified log current signal to the amplified log voltage signal. The controller may be configured to calculate log impedance by subtracting the amplified log current signal from the amplified log voltage signal. The electrosurgical generator may operate without calculating an antilog, e.g., the gain coefficients may change based upon a log power or a log impedance.
• According to an aspect of the present disclosure, a method of controlling an electrosurgical generator is provided. The method includes the initial steps of supplying electrosurgical energy to tissue, determining a current of the electrosurgical energy, and determining a log of the determined current of the electrosurgical energy, determining a voltage of the electrosurgical energy. The method further includes the steps of determining a log of the determined voltage of the electrosurgical energy, and controlling the electrosurgical energy as a function of the log of the determined current and the log of the determined voltage.
• The method may further include the steps of applying a proportional-integral-derivative transfer function using the log of the determined current, the log of the determined voltage, a log impedance, and/or a log power. The method may further include the steps of adjusting the electrosurgical energy as a function of the applied proportional-integral-derivative transfer function, and adjusting a gain coefficient of the proportional-integral-derivative transfer function. The proportional-integral-derivative transfer function may be applied to a comparison between a setpoint and one of the log of the determined current, the log of the determined voltage, the log impedance, and the log power (e.g., feedback is subtracted from the setpoint to provide an error signal).
BRIEF DESCRIPTION OF THE DRAWINGS
• Objects and features of the presently-disclosed logarithmic amplifier, electrosurgical generator including the same, and a method of controlling an electrosurgical generator using the same will become apparent to those of ordinary skill in the art when descriptions of various embodiments thereof are read with reference to the accompanying drawings, of which:
• FIG. 1 shows an illustration of an electrosurgical system having an electrosurgical generator that uses logarithmic amplifiers in accordance with an embodiment of the present disclosure;
• FIG. 2 shows a block diagram of the electrosurgical generator ofFIG. 1 that uses logarithmic amplifiers in accordance with an embodiment of the present disclosure;
• FIG. 3 shows a block diagram of the control system of the electrosurgical generator ofFIG. 2 in accordance with an embodiment of the present disclosure;
• FIG. 4A shows a capacitor divider network for measuring current in accordance with an embodiment of the present disclosure;
• FIG. 4B shows a capacitor divider network for measuring voltage in accordance with an embodiment of the present disclosure;
• FIG. 5 shows a sensor configuration for a microwave generator in accordance with an embodiment of the present disclosure; and
• FIG. 6 shows a flow chart diagram of a method for controlling an electrosurgical generator using logarithmic amplifiers in accordance with an embodiment the present disclosure.
DETAILED DESCRIPTION
• Hereinafter, embodiments of a logarithmic amplifier, an electrosurgical generator including the same, and a method of controlling an electrosurgical generator using the same of the present disclosure are described with reference to the accompanying drawings. Like reference numerals may refer to similar or identical elements throughout the description of the figures. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.
• Various embodiments of the presently-disclosed logarithmic amplifier are suitable for use in electrosurgical generators and electrosurgical systems including the same. The presently-disclosed logarithmic (log) amplifier embodiments can be used to amplify and compress a signal which varies over a large dynamic range into a suitable log amplifier output range, e.g., 0 volts to about 3 volts.
• FIG. 1 shows an illustration of a bipolar and monopolarelectrosurgical system100 in accordance with an embodiment of the present disclosure. Theelectrosurgical system100 includes agenerator102 that uses one or more logarithmic amplifiers (described below).
• In some embodiments, thegenerator102 is an electrosurgical generator adapted to supply electrosurgical energy to tissue, e.g., to meet the needs of the surgeon or surgical team for hospital, surgery center, and/or office-based procedures. Thegenerator102 may be adapted for use to perform monopolar and/or bipolar electrosurgical procedures including vessel-sealing procedures and/or other procedures. Thegenerator102 may include a plurality of outputs (e.g.,terminals104 and106) for interfacing with various electrosurgical instruments (e.g., a monopolaractive electrode108, areturn pad110, bipolarelectrosurgical forceps112, a footswitch (not shown), etc.). Thegenerator102 may additionally, or alternatively, include electronic circuitry that is configured to generate radio-frequency power (or other type of surgical energy, e.g., light energy, microwave energy, ultrasonic energy, etc.) specifically suited for various electrosurgical modes (e.g., cutting, blending, division, etc.) and procedures (e.g., monopolar treatment, bipolar treatment, vessel sealing, etc.). Thegenerator102 may have a power range. In some embodiments, thegenerator102 may have a power range from about 1 milliwatt (mW) (1×10⁻³watts) to about 150 kilowatts (kW) (1×10³watts).
• Thesystem100 includes a monopolarelectrosurgical instrument114 having one ormore electrodes108 for treating tissue of a patient (e.g., electrosurgical pencil, electrosurgical cutting probe, ablation electrode(s), etc.). Electrosurgical RF energy is supplied to theinstrument114 by thegenerator102 via a transmission line, e.g.,supply line116. As mentioned above, “transmission line” generally refers to any transmission medium that can be used for the propagation of signals from one point to another.Supply line116 is operably connected to anactive terminal104 of thegenerator102, allowing theinstrument114 to coagulate, ablate, or otherwise treat tissue. The energy is returned fromelectrode108 through tissue to thegenerator102 via a transmission line, e.g., via areturn line118 of thereturn pad110, at areturn terminal106 of thegenerator102. Theactive terminal104 and thereturn terminal106 may include connectors (not shown) configured to interface with plugs (not shown) of theinstrument114 and thereturn electrode110, which are disposed at the ends of thesupply line116 and thereturn line118, respectively.
• Thesystem100 includesreturn electrodes120,122 withinreturn pad110 that are arranged to minimize the chances of tissue damage by maximizing the overall contact area with the patient's tissue. Thegenerator102 and thereturn electrode110 may additionally, or alternatively, be configured for monitoring contact quality to ensure that sufficient contact exists therebetween to further minimize chances of tissue damage.
• Thesystem100 generally includes a bipolarelectrosurgical forceps instrument112 having one or more electrodes (e.g.,electrodes124 and126) for treating tissue of a patient. In some embodiments, as shown inFIG. 1, theinstrument112 includes opposingjaw members134,136 having anactive electrode124 and areturn electrode126 disposed therein, respectively. Theactive electrode124 and thereturn electrode126 are connectable to thegenerator102 through atransmission line128, e.g., a cable that includes asupply line130 and areturn line132 coupled to theactive terminal104 and thereturn terminal106, respectively. Theinstrument112 is coupled to thegenerator102 at a connector having connections to theactive terminal104 and the return terminal106 (e.g., pins) via a plug (not shown) disposed at the end of thetransmission line128, wherein the plug includes contacts from thesupply line130 and thereturn line132.
• Thegenerator102 may be any suitable type (e.g., electrosurgical, microwave, etc.) and may include a plurality of connectors to accommodate various types of electrosurgical instruments (e.g.,instrument114,electrosurgical forceps112, etc.). Thegenerator102 may be configured to operate in a variety of modes such as ablation, monopolar and bipolar cutting, coagulation, and other modes. Thegenerator102 may include a switching mechanism (e.g., relays) to switch the supply of energy, e.g., RF energy, between the connectors, such that, for instance, when theinstrument114 is connected to thegenerator102, only the monopolar plug receives RF energy. Theactive terminal104 and returnterminals106 may be coupled to a plurality of connectors (e.g., inputs and outputs) of thegenerator102 to power a variety of instruments.
• Thegenerator102 may include a user interface, e.g., configured to provide user-input capabilities and/or capabilities for simplified use and/or programming of thegenerator102. Thegenerator102 includes suitable input controls (e.g., buttons, activators, switches, touch screen and the like) adapted to enable a user to selectively configure one or more operating parameters of thegenerator102, or component thereof, e.g., depending upon a particular purpose and/or to achieve a desired surgical outcome. In addition, thegenerator102 may include one or more display screens, such as a flat-panel display, e.g., an LCD (liquid crystal display), plasma display panel (PDP), organic light emitting diode (OLED), or electro-luminescent display (ELD), for providing the user with a variety of output information (e.g., intensity settings, treatment complete indicators, etc.). The controls allow the user to adjust power of the RF energy, waveform, and/or other parameters to achieve the desired waveform suitable for a particular task (e.g., coagulating, tissue sealing, intensity setting, etc.). Theinstruments112,114 may also include a plurality of input controls that may be redundant with certain input controls of thegenerator102. Placing the input controls at theinstruments112,114 allows for easier and faster modification of RF energy parameters during the surgical procedure without requiring user interaction with thegenerator102.
• Referring to the drawings,FIG. 2 shows a block diagram of theelectrosurgical generator102 ofFIG. 1 in accordance with an embodiment of the present disclosure.Electrosurgical generator102 includes acontroller200, a high-voltage power supply202 (HVPS), a radio-frequency (RF)output stage204, and logamplifiers206,208. Thecontroller200 includes aprocessor unit210 and amemory212. Theprocessor unit210 may include any type of computing device, computational circuit, or any type of processor or processing circuit capable of executing a series of instructions that are stored in a computer-readable storage medium (e.g., memory212), which may be any device or medium that can store code and/or data. In some embodiments, theprocessor unit210 may be any suitable microcontroller, microprocessor (e.g., Harvard or Von Neumann architectures), PLD, PLA, or other suitable digital logic. In some embodiments, thememory212 may be volatile, non-volatile, solid state, magnetic, or other non-transitory computer-readable medium.
• Thecontroller200 may include various circuitry (e.g., amplifiers, buffers, and the like) to interface theprocessor unit210 to circuitry within theelectrosurgical generator102. Thecontroller200 receives various feedback signals that are analyzed by theprocessor unit210 to provide control signals in response thereto. The control signals from thecontroller200 control theHVPS202 and theRF output stage204 to provide electrosurgical energy to tissue, which is represented by aload R_L216.
• TheHVPS202 includes apower circuit214. Thepower circuit214 supplies a suitable electric current to theRF output stage204. TheRF output stage204 converts the current from thepower circuit208 to electrosurgical energy for application to theload R_L216. In some embodiments, theHVPS202 provides a DC signal to theRF output stage204, which, in turn, generates the electrosurgical energy using a push-pull transistor configuration coupled to a primary side of a step-up transformer (not shown).
• As previously mentioned, thecontroller200 receives feedback from various feedback signals that are analyzed by theprocessor unit210 to provide control signals in response thereto. Thecontroller200 may receive a log current from thelog amplifier206 and/or a log voltage from thelog amplifier208. In some embodiments, thecontroller200 receives a current signal from acurrent sensor218 after amplification by thelog amplifier206. Thecontroller200 may additionally, or alternatively, receive a voltage signal from avoltage sensor220 after amplification by thelog amplifier208.
• Logamplifiers206,208 may be log amplifiers that saturate with negative input, and/or may be output polarity independent of input polarity (e.g., a detecting log amp). Logamplifiers206,208 may additionally, or alternatively, be true log amplifiers (e.g., may have a symmetrical response to positive or negative signals). Additionally or alternatively, thelog amplifiers206 and208 may be successive detection log amplifiers.
• Thecontroller200 receives the log current and log voltage signals fromlog amplifiers206 and208, respectively, and controls the high-voltage power supply202 in response thereto. In some embodiments, thecontroller200 may be a proportional-integral-derivate controller (“PID controller”).
• Thecontroller200 may be adapted to control the output of theelectrosurgical generator102 to achieve a target log voltage, a target log current, a target power, a target log power, and/or a target log impedance, e.g., a target log tissue impedance. Thecontroller200 may be configured to calculate log power by adding the amplified log current signal from thelog amplifier206 to the amplified log voltage signal from thelog amplifier208. Thecontroller200 may be configured to calculate the log impedance by subtracting the log current signal received from thelog amplifier206 from the log voltage signal received from thelog amplifier208. In some embodiments of the present disclosure, thecontroller200 converts an amplified signal from thelog amplifier206 and/or thelog amplifier208 to an RMS value or an antilog of the amplified sensor signal. In other embodiments of the present disclosure, thecontroller200 does not calculate an antilog of either of the signals from thelog amplifier206 or thelog amplifier208.
• Thecontroller200 may have one or more variable gain coefficients, e.g., a PID controller may vary one or more of a proportional gain coefficient, an integral gain coefficient, or an integral gain coefficient. In some embodiments, the one or more coefficients may be varied based upon a log current, a log voltage, a log impedance, and/or a log power.
• FIG. 3 shows a block diagram of thecontrol system300 of the electrosurgical generator ofFIG. 2 in accordance with an embodiment of the present disclosure. Thecontrol system300 includes asummer302, aPID transfer function304, a PID coefficient table306,feedback308, and asetpoint310.
• In some embodiments, thesummer302, theRID transfer function304, the PID coefficient table306, thefeedback308, and thesetpoint310 are implemented by an operative set of processor executable instructions configured to be executed by at least oneprocessor210 within memory212 (seeFIG. 2). Thememory212 is a non-transitory computer readable (e.g., readable by processor unit210) medium. In other embodiments, thesummer302, thePID transfer function304, the RID coefficient table306, thefeedback308 and thesetpoint310 may be implemented in software, hardware, software in execution, firmware, bytecode, microcode, PLDs, FPGAs, PALs, a microprocessor, a microcontroller, or some combination thereof.
• Thesetpoint310 may be a target log voltage, log current, log impedance, log power, or the like. Additionally or alternatively, thesetpoint310 may be a target voltage, current, power, or impedance.
• Thesetpoint310 is provided tosummer302. Thesummer302 compares thesetpoint310 to thefeedback308. Thesetpoint310 may be a desired or target value, and thefeedback308 provides the actual value being delivered to theload R_L216.
• Thefeedback308 corresponds to thesetpoint310. For example, if thesetpoint310 is a target log voltage, then thefeedback308 provides the signal from theamplifier208, which is the log voltage fromload R_L216.
• Thefeedback308 may calculate log power by adding the amplified log current signal received from thelog amplifier206 to the amplified log voltage signal received from thelog amplifier208. Thefeedback308 may calculate the log impedance by subtracting the log current signal received from thelog amplifier206 from the log voltage signal received from thelog amplifier208. In some embodiments of the present disclosure, thefeedback308 converts an amplified signal from thelog amplifiers206,208 to an RMS value or an antilog of the amplified sensor signal. In other embodiments of the present disclosure, thefeedback308 does not calculate an antilog from either of the signal from thelog amplifiers206 or the signal from thelog amplifier208. As previously mentioned, thefeedback308 is provided to thesummer302.
• Thesummer302 compares thesetpoint310 to thefeedback308 and generates an error signal. The error signal is the difference between thesetpoint310 and thefeedback308. Typically, the summer subtracts the feedback from the setpoint310 (also referred to as negative feedback). The error signal is fed into thePID transfer function304.
• ThePID transfer function304 adds proportional, integral, and derivative terms together and outputs the results to theload R_L216. Each term includes a coefficient. In some embodiments, the proportional term is the error signal multiplied by a proportional coefficient, the integral term is the integration of the error signal multiplied by an integral coefficient, and the derivative term is the derivative of the error signal multiplied by a derivative coefficient. In some embodiments, the proportional, integral and derivative terms are added together and applied to theload R_L216. AlthoughFIG. 3 shows the output of thePID transfer function304 as being directly applied to theload R_L216, various driver circuitry may be used (e.g., an analog-to-digital converter (not shown), theHVPS202 and/or the RF output stage203 as shown inFIG. 2).
• The PID coefficients (also referred to as RID gain coefficients) are stored within the PID coefficients table306. The PID coefficients table306 provides the PID coefficients to thePID transfer function304. The PID coefficients table306 can vary one or more coefficients of thePID transfer function304 based upon the error signal from thesummer302, a signal from thelog amplifiers206,208, a log voltage, a log current, a log power, a log impedance, and the like. Additionally or alternatively, the PID coefficients from table306 may be varied as a function of the voltage, current, power, of the electrosurgical energy as applied to theload R_L216, or the impedance of the load R_L216 (e.g., tissue impedance).
• In some embodiments, the PID coefficients table306 may have three ranges for log power with each range having three different PID gain coefficients, and the PID coefficients table306 may load the PID gain coefficients in accordance with the current power range of the log power.
• FIG. 4A shows acapacitor divider network400 for measuring current in accordance with an embodiment of the present disclosure. Thenetwork400 includes a configuration ofcapacitors402,404,406,408,410. Referring toFIGS. 2 and 4, thecapacitor402 is coupled between thenodes412,414. Thenodes412,414 may be coupled between the terminal104 and ground, respectively, to measure the voltage applied to theload R_L216. Thecapacitor402 is used as a current sense element. As current goes through thecapacitor402, it produces a voltage V, which may be expressed as
• $V=\frac{I·\mathrm{dt}}{C},$
• where I is the current, dt is the switching time of theRF stage428 and C is thecapacitance value402. Thecapacitor402 may be used as the low-frequency blocking capacitor for safety standards.
• Additionally or alternatively, thenodes412,414 may be coupled between theterminals104,106, respectively, to measure the current applied to load R_L216 (seeFIG. 2). The current through thecapacitor402 may be derived by measuring the voltage across thecapacitor402 when the capacitance of thecapacitor402 is known or measured.
• In some embodiments, as shown inFIG. 4A, thecapacitors402,404,406,408,410 are arranged in an H configuration and function as a capacitor divider network. Thecapacitors404 and408 are used for isolating the ground of theRF stage426 from thenon-isolated ground427 of the system. Thecapacitors406 and410 are used to reduce the signal level I_Xgoing to the log amplifier and reference the signal to thesystem ground427.
• In some embodiments of the present disclosure, optocouplers and/or isolation transformers are used to provide an isolation barrier between the patient and the ground of the generator. The component for sensing current402 may be the current sensor218 (FIG. 2). The components forsensing voltage419,421,422,423 may be thevoltage sensor220 that is electrically coupled to theRF output stage204. Thelog amplifier206 measures the voltage difference between the nodes of: (1) thenode418 betweencapacitors404 and406; and (2) thenode420 betweencapacitors408 and410. Thecapacitor402 may be split into various parallel or serial capacitors, e.g., to adjust creepage, clearance, and voltage breakdown for the isolation barrier between the patient and ground. Thedivider network400 formed by thecapacitors404,406,408,410 reduces the voltage measured by thelog amplifier206 by a predetermined amount and is a function of the frequency of the electrosurgical energy and the capacitance of thecapacitors402,404,406,408,410. Thecapacitors402,404,406,408,410 provide isolation between a ground of the electrosurgical generator102 (seeFIG. 2) and the patient P, e.g., to prevent voltage breakdown of theseveral capacitors402,404,406,408,410 during typical use between the patient and a ground of theelectrosurgical generator102.
• In some embodiments of the present disclosure, a transformer (not shown) may be interposed between thecapacitor402 and thelog amplifier206 to provide isolation therebetween and/or to step-down the voltage of the electrosurgical energy prior to measurement by thelog amplifier206.
• FIG. 4B shows acapacitor divider network410 for measuring voltage in accordance with an embodiment of the present disclosure.FIG. 4B shows the isolation of theground426 of theRF output stage428 to thesystem ground427 through thecapacitors419 and422. Thecapacitors419 and422 transfer the voltage across the isolation boundary. Thecapacitors421 and423 reduce the signal level V_X1and V_X2going to thelog amplifier208 and reference the voltage tosystem ground427. Theactive output424 of the generator and thereturn output425 of the generator are connected to the patient, represented asR_L429. The two voltages V_X1and V_X2can fully monitor the output voltage across the patient and serve as redundant sensors.
• FIG. 5 shows asensor configuration500 for a microwave generator in accordance with an embodiment of the present disclosure that provides a dual directional coupler suitable for measurement of forward and reflective voltage. Thesensor configuration500 includes a first line L₁defined between anode543 and thesystem ground427, a second line L₂defined betweennodes541 and540, and a third line L₃defined between anode542 andsystem ground427
• Theoutput541 of agenerator540 is a coupled line that measures the forward voltage and543 measures thereflective voltage542.Termination resistors544 and545 are provided for the signal lines L₁and L₃, respectively. The space between the lines L₁and L₂and the space between the lines L₂and L₃determines the signal strength going to the log amplifier. This signal strength is also influenced by the length of the lines for nodes L₁and L₂, the termination resistance444,445, and the width of traces for lines L₁and L₂.
• FIG. 6 shows a flow chart diagram of amethod600 for controlling an electrosurgical generator using a log amplifier in accordance with an embodiment the present disclosure.Method600 includes steps602-620. In step602, electrosurgical energy is supplied to tissue.
• Instep604, the current of the electrosurgical energy is determined. Instep606, the log of the determined current of the electrosurgical energy is determined. For example,Step606 may use thelog amplifier206 ofFIG. 2.
• Instep608, the voltage of the electrosurgical energy is determined. Instep610, the log of the determined voltage of the electrosurgical energy is determined. Step608 may use thelog amplifier208 ofFIG. 2.
• Step612 includessteps614 through620. Step612 controls the electrosurgical energy as a function of the log of the determined current and the log of the determined voltage. Instep614, a gain coefficient of the proportional-integral-derivative transfer function (“PID transfer function”) is adjusted. The PID transfer function ofmethod600 may be thePID transfer function304 ofFIG. 3. Instep616, a PID transfer function is applied using one or more of the log of the determined current, the log of the determined voltage, a log impedance, and a log power.
• Instep618, the PID transfer function is applied to an error generated by comparing a setpoint to one or more of the determined current, the log of the determined voltage, the log impedance, and the log power.Steps616 and618 may be integrated together or may be separate.
• Instep620, the electrosurgical energy is adjusted as a function of the applied RID transfer function. Thereafter, a manual or automatic deciding step is included instep622 to determine whether to repeat themethod600 or to stop the application of the electrosurgical energy to tissue. In some embodiments, a pressed button on a portable electrosurgical generator causes themethod600 to repeat until the button is released, then themethod600 will stop; that is, the releasedbutton causes method600 to stop.
• Although embodiments have been described in detail with reference to the accompanying drawings for the purpose of illustration and description, it is to be understood that the inventive processes and apparatus are not to be construed as limited thereby. It will be apparent to those of ordinary skill in the art that various modifications to the foregoing embodiments may be made without departing from the scope of the disclosure.

Claims (20)

What is claimed is:

1. A control system for controlling an electrosurgical generator, comprising:

a sensor to generate a sensor signal;

a log amplifier coupled to the sensor to amplify and compress the sensor signal; and

a controller to generate an output signal as a function of the amplified sensor signal.

2. The control system according toclaim 1, further comprising a summer to sum a setpoint and a negation of the amplified signal from the log amplifier to generate an error, wherein the controller generates the output signal as a function of the error.

3. The control system according toclaim 1, wherein the controller is adapted to generate electrosurgical energy thereby defining the output signal.

4. The control system according toclaim 1, wherein the sensor comprises a plurality of capacitors forming a voltage divider network coupled to the output signal, wherein the sensor signal includes a voltage of a capacitor of the divider network.

5. The control system according toclaim 1, wherein the controller is a proportional-integral-derivative controller.

6. The control system according toclaim 5, wherein the proportional-integral-derivative controller has at least one variable gain coefficient.

7. The control system according toclaim 5, wherein the proportional-integral-derivative controller varies a proportional gain coefficient, an integral gain coefficient and a derivative gain coefficient.

8. An electrosurgical generator, comprising:

an RF output stage configured to supply electrosurgical energy to tissue;

a current sensor configured to sense a current of the electrosurgical energy, wherein the current sensor generates a current signal corresponding to the current of the electrosurgical energy;

a first log amplifier configured to amplify and compress the current signal;

a voltage sensor configured to sense a voltage of the electrosurgical energy and generate a voltage signal in response thereto;

a second log amplifier configured to amplify and compress the voltage signal; and

a controller configured to receive the amplified and compressed voltage signal and the amplified and compressed current signal and control the generation of the electrosurgical energy as a function of the amplified and compressed voltage signal and the amplified and compressed current signal.

9. The electrosurgical generator according toclaim 8, wherein the controller calculates a sum of a log voltage signal and a log current signal to compute a measured log power.

10. The electrosurgical generator according toclaim 8, further comprising a capacitor divider network for measuring the current of the electrosurgical energy.

11. The electrosurgical generator according toclaim 8, wherein the voltage sensor comprises a plurality of capacitors forming a capacitor divider network coupled to the RF output stage for measuring the voltage of the electrosurgical energy.

12. The electrosurgical generator according toclaim 8, further comprising a dual directional coupler adapted for measurement of forward and reflective voltage.

13. The electrosurgical generator according toclaim 8, wherein the controller is a proportional-integral-derivative controller.

14. The electrosurgical generator according toclaim 13, wherein the proportional-integral-derivative controller has at least one variable gain coefficient.

15. The electrosurgical generator according toclaim 13, wherein the proportional-integral-derivative controller varies a proportional gain coefficient, an integral gain coefficient and a derivative gain coefficient.

16. The electrosurgical generator according toclaim 13 wherein at least one gain coefficient varies as a function of at least one of the amplified voltage signal and the amplified current signal.

17. A method of controlling an electrosurgical generator, comprising the steps of:

supplying electrosurgical energy to tissue;

determining a current of the electrosurgical energy;

determining a log of the determined current of the electrosurgical energy;

determining a voltage of the electrosurgical energy;

determining a log of the determined voltage of the electrosurgical energy; and

controlling the electrosurgical energy as a function of the log of the determined current and the log of the determined voltage.

18. The method according toclaim 17, further comprising the step of:

applying a proportional-integral-derivative transfer function using at least one of the log of the determined current, the log of the determined voltage, a log impedance and a log power; and

adjusting the electrosurgical energy as a function of the applied proportional-integral-derivative transfer function.

19. The method according toclaim 17, further comprising the step of adjusting a gain coefficient of the proportional-integral-derivative transfer function.

20. The method according toclaim 17, wherein the proportional-integral-derivative transfer function is applied to a comparison between a setpoint and at least one of the log of the determined current, the log of the determined voltage, the log impedance and the log power.

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